The present invention relates to a method and apparatus for depositing materials on a moving web in precise shapes or patterns, in general, and to such method and apparatus for preventing a deterioration in the pattern contours of materials being continually deposited on such a web for extended periods of time, in particular.
Applying coating materials to a moving web through a pattern forming mask for extended periods of time often produces unacceptable changes in the shape being formed by the mask pattern. This shape change is primarily due to an excessive buildup of coating materials on surfaces immediately adjacent and/or at the edges of the pattern-forming mask openings. Such excessive coating-material buildup eventually reduces mask opening size. If the mask openings are relatively large, reductions in mask opening size may have little or no meaningful effect on material shape. However, when mask opening size is extremely small, such as on the order of a few thousands of an inch, small changes in mask opening size can have a substantial negative effect on coating material shape. If the coating mask is periodically removed from the coating apparatus and thoroughly cleaned, changes in mask opening contours can be avoided. However, in addition to this being a time-consuming process, such a process greatly reduces the amount of time coating apparatus is available for coating purposes, and therefore, the volume of coated product that can be produced by such apparatus in a given period of time. Periodic cleaning of a coating mask employed in continuous coating apparatus would obviously produce the greatest reduction in coated-product output volume.
One very common material pattern that can be deposited on a moving web, through a coating mask, by presently available apparatus for extended periods of time before the coating mask needs cleaning is that of a continuous coating material stripe. Apparatus capable of depositing such a stripe or a plurality of such stripes on a moving web is shown in U.S. Pat. No. 3,866,565 to RIDOUT. The apparatus comprises a plurality of spaced-apart wheels or discs mounted for rotation on a common shaft, with coating material in the form of a continuous stripe being deposited on web material presented at the peripheries of said spaced-apart wheels. Coating apparatus of this type may be capable of placing relatively large width stripes on a moving web for extended periods of time before wheel or disc cleaning might be necessary. However, it would be difficult if not impossible to produce such coating apparatus that would be capable of simultaneously placing large numbers of stripes having stripe densities on the order of 40 stripes per inch on a moving web whether or not such cleaning would be necessary, primarily because of the extremely small disc thicknesses that would be required to produce such densities. Stripe densities on this order of magnitude are required in, for example, the manufacture of liquid crystal displays.
The primary object of the present invention is, therefore, to provide a method and apparatus for continuously cleaning a coating mask employed in web coating apparatus for the purpose of placing coating materials on a moving web surface having predetermined contours or shapes.
Another object of the present invention is to provide a method and apparatus for maintaining the definition or contours of a coating mask pattern for extended periods of time.
A further object of the present invention is to provide a method and apparatus for maintaining the definition of extremely small pattern openings in a web coating mask.
Other objects, features, and advantages of the present invention will be readily apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawings.